The invention relates generally to shellfish processing and more particularly to apparatus and methods for deheading shrimp with hydrodynamic forces.
Deheading shrimp by hydrodynamic force is known from U.S. Pat. No. 5,195,921, “Apparatus for Deheading and Cleansing Shrimp,” issued Mar. 23, 1993. In that patent, a shrimp-laden fluid is pumped through conduit that abruptly narrows. The abrupt decrease in the cross-section of the conduit causes the flow to accelerate through the narrow cross section according to the Venturi Effect. Hydrodynamic forces caused by the change in cross section tend to detach heads from shrimp. The cross section of the conduit in the patent is circular along its entire length. When a pipe with a four-inch diameter is used as the main conduit, the diameter of the narrow region is even smaller. Shrimp, whose outer dimensions are greater than the diameter of the narrow region, tend to bump into the narrowing conduit. The collisions with the conduit walls can damage the shrimp, especially fragile cold-water shrimp. As shown in FIGS. 1A and 1B, cold-water shrimp 10 have a long, thin sixth segment 12 that is easy to damage. The joint 14 between the third and fourth segments is also susceptible to damage. In general, the muscle tissue in cold-water shrimp is much weaker than in the sturdier warm-water shrimp. When a cold-water shrimp 10 approaches the narrow region of the conduit side-on, as opposed to head or tail first, it bangs into the sides of the opening into the narrow region. The collisions do help remove the head, but they also can cause the shrimp to break at its weak spots.